Op amp

Thread Starter

MURUGESAN K

Joined Jul 16, 2013
5
Dear sir,

I am using an Op Amp uA 741.

I am having 2 Dc power supply unit(unit A,Unit B). I am giving +12V and -12 V (+Vcc,-Vcc) to the op amp by using power supply unit A, and i am using power supply unit B to give input (+v,-v) to the same op amp. Which supply unit's ground should i choose as reference to take output voltage?
 
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LvW

Joined Jun 13, 2013
1,752
How is it possible to use one single unit (in your case A) to feed +Vcc as well as -Vcc ?
Of course, you must use A for +Vcc and B for -Vcc. Both supplies are to be referenced to ground. For the signal input you need, of course, another signal source (ac or dc).
 

t06afre

Joined May 11, 2009
5,934
This is the basic method of creating a split supply using two separate powers. In this case two batteries. But the setup is valid for your situation
 

LvW

Joined Jun 13, 2013
1,752
The diagram as given by t06afre reveals the critical point.
Following this diagram, you now have a voltage of 18 Volts between both supply pins of the opamp.
And now you can ask: Why not 12V as described in your question ?
The important aspect is the ground connection in the middle of the total voltage.
Your opamp must "know" where the common reference point is (called "ground") because the input signal must be referenced to such a common potential rail (ground).

Of course, you can use one single supply voltage only - however, not BETWEEN both supply pins but between one of these pins and ground. In this case, the desired dc operating point (dc quiescent output voltage) must be again somewhere in the middle of this voltage. Thus, your output can swing - caused by an input signal - in both directions from this operatimg point.
But you must know that in this case you need some additional provisions (bias circuitry) at the opamp input.
My recommendation: Start an internet search with the keyword "single supply operation".
 

Thread Starter

MURUGESAN K

Joined Jul 16, 2013
5
How is it possible to use one single unit (in your case A) to feed +Vcc as well as -Vcc ?
Of course, you must use A for +Vcc and B for -Vcc. Both supplies are to be referenced to ground. For the signal input you need, of course, another signal source (ac or dc).
It is a Dual output Dc power supply unit. Each supply unit having 3 terminals.

1. +12 v out
2. -12 v out
3.Ground.

My doubt is which ground( unit A's Ground or unit B's Ground ) should i choose while taking output from Op amp .
 

t06afre

Joined May 11, 2009
5,934
If your power supply is of a dual or split type supply. Like you describe in post #5. You will only need one of the latter supply to power your opamp circuit with +/- 12 volt. The output from the opamp should use ground as reference point.
 
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